In today's rapidly advancing semiconductor manufacturing industry, copper is becoming increasingly favored as the interconnect material of choice. The use of copper as the interconnect medium maximizes device speed but also requires special processing because of difficulties in patterning, corrosion concerns, the rapid oxidation of exposed copper surfaces and the tendency of copper alloys to form hillocks.
When a copper alloy interconnect becomes oxidized, the quality of a contact made to the copper surface decreases, for example, contact resistance increases. Therefore, it is desirable to remove copper oxides that form on copper surfaces, even native copper oxides that form in the brief duration between processing operations. Various treatment procedures have been used to remove the oxidized portion of the copper film and the conventional procedures enjoy various degrees of success in removing part of the oxidized copper. When an uneven or discontinuous copper oxide is not completely removed by such a treatment operation designed to remove the copper oxide, subsequent thermal heat treatment processes such as conventional annealing processes cause the formation of hillocks preferentially at void locations between intact portions of the Cu oxide that remains over the copper. A high concentration of hillocks may cause future patterning problems and hillocks invariably cause shorting problems between the copper and overlying layers of conductive material as the high aspect ratio of the hillocks enables them to protrude through subsequently deposited and planarized insulating materials. In contrast, non-oxidized copper surfaces are resistant to hillock formation during subsequent thermal processing.
As such, it would be desirable to provide a copper surface treatment procedure that produces a copper structure free of oxides and hillocks and enables a dielectric film to be subsequently formed over the copper surface that remains oxide-free and hillock-free. The present invention is directed to and provides such procedures.